Although polypropylene has excellent shaping processability, water resistance, oil resistance, acid resistance, alkali resistance, and so forth, it is also known to have poor heat resistance and rigidity. Accordingly, a known technique of compounding polyphenylene ether with polypropylene may be adopted to obtain a resin composition having enhanced properties in terms of heat resistance, rigidity, and so forth.
Examples of techniques for further imparting flame retardance on this resin composition include a commonly adopted technique of adding a halogen-containing compound and antimony trioxide. However, since flame retardants such as halogen-containing compounds and antimony trioxide are undesirable from a viewpoint of environmental health, there is demand for improved flame retardance imparting techniques, such as techniques using flame retardants that do not contain halogen-containing compounds, antimony trioxide, or the like.
Examples of known techniques for responding to this demand include a technique of compounding a flame retardant such as a metal salt of phosphinic acid with a polyphenylene ether resin and a polypropylene resin (for example, refer to PTL 1 to 3). Moreover, PTL 4 and 5 disclose the use of another flame retardant or flame retardant synergist in addition to a metal salt of phosphinic acid to obtain a resin composition having even better flame retardance.